1. Field of the Invention
The present invention relates generally to fluid monitors for detecting the presence of a substance in a fluid and, more particularly, to a method and device for detecting the presence of an antigenic substance in a fluid.
2. Prior Art
Determining the presence of a suspect substance in a liquid sample is a problem that has been addressed by many technologies. The methodology most commonly used for detecting such substances involves using one or more antibodies that have been matched to an antigenic binding site or sites characterizing the suspect substance. These matched antibodies must be colored or otherwise tagged in a way that is physically distinguishable from some type of control in which the antigen/antibody reaction has been prevented from taking place.
Such prior art immunological detection procedures vary somewhat, but generally involve isolating a small portion of the liquid sample, exposing it to the tagged antibody, and comparing the resultant reactions (or lack thereof) with a control. Notwithstanding false readings, a significant difference between the sample and the control indicates the presence of the suspect antigen in the liquid.
Methods for making and harvesting monoclonal or polyclonal antibodies that have a specific avidity for a given antigen are well known in the art. Prior art detection methodologies employing antigen-antibody binding require a multiple stage analysis. This may be accomplished by either directing the sample fluid along a flow path from the reaction region to a xe2x80x9cdeveloperxe2x80x9d region, or by physically moving the sample from one region to another. Such methods have presented many problems. The challenge has been to design a system with sufficient test sample fluid throughput so that it is possible for the required reactions to occur. Such devices must be discarded after only one use. There remains a need for a detection device and method that can be used to monitor a fluid for the presence of a substance and which can be reused until the substance is detected.
The present invention is a device for detecting the presence of an antigen of interest in a liquid. The device is comprised of a hollow casing having an interior volume defined by the hollow casing. A plurality of beads is disposed within therein fills the interior volume. The beads have a measurably distinguishing attribute associated therewith, preferably a distinctive color, and have antibodies attached thereto that are capable of binding to the antigen of interest. A portion of the casing is a permeable screen enabling the diffusion of both the test fluid and the antigen therethrough but retaining the beads within the interior volume. A test strip disposed on an interior surface of the casing comprises a collection region disposed on a portion thereof. The collection region has at least one antibody capable of binding to the antigen of interest and incapable of binding to the beads attached thereto. When the device is dipped into the liquid to be tested, the liquid enters the interior volume through the permeable screen and if the antigen of interest is present within the fluid-filled interior volume of the casing, the beads become attached to the collection region by virtue of their common bond with the antigen of interest, thereby concentrating the colored beads in the collection region. The strip further includes a control region disposed thereon having the ability to retain its original state regardless of the presence or absence of the antigen of interest. The phrase xe2x80x9ccontrol regionxe2x80x9d, as used herein, means a region of the test strip lacking antigen-specific antibodies bound thereto. It provides a comparison with the collection region so that a reasonable determination of the presence of the suspect antigen can be made.
It is a first object of this invention to provide a small, simple device that can be easily manufactured, is usable by any member of the general public, and provides a reliable test for the presence of a specific antigen in a liquid sample.
It is a further object of the invention to provide a device meeting the above objective that can be used to monitor a fluid for the presence of the specific antigen over an extended period of time.
An example of a current application of the present monitoring device and method for solving a current social problem is the monitoring beverages for the presence of GHB or rohypnol, the so called date rape drugs. Other applications include medical analysis (i.e., detecting a substance in various body fluids), drug testing/screening, municipal water testing and pregnancy testing. The monitoring device is also suitable for biological or chemical warfare applications in that it can be designed to test for particular pathogens or chemicals suspected or known to be used in such situations. It is particularly useful to hikers and other outdoor enthusiasts for the screening of water supply sources.
The present device is not a flow system. Although the sample fluid must enter the interior volume of the device in order to be tested for the presence of a substance, the fluid does not have to be routed along a prescribed flow path or be transported into a developer region or be rinsed or washed in order for the device to operate. Thus, questions of fluid sample xe2x80x9cthroughputxe2x80x9d that plague the prior art are rendered moot with the present device. The present device is unique in that it continuously monitors any liquid in which it is placed until such time as the indicator system either undergoes denaturization (i.e., becomes inoperable as a detector), or detects the suspect antigen. Accordingly, the present monitoring device can be used to test several different volumes of liquid, such as, for example, alcoholic beverages, in real time during its effective lifetime. Further, the present device will not introduce any reactants, either toxic or otherwise, into the sample being tested. In the case of a positive reading, the device serves to contain the suspect liquid as evidence of the presence of an antigen, which may indicate tampering, or for subsequent confirmatory analysis.